Upper Electrode Sulfur Control for Electron Emission Stability
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Solution Overview
Problem
Cold cathode type thin film electron sources in image display devices are prone to contamination from sulfur, chlorine, fluorine, nitrogen, and carbon-based materials, leading to decreased electron emission brightness due to adhesion of these elements on the upper electrode, which affects the work function and electron emission characteristics.
Innovation Solution
The use of elements from Group VIII or Group Ib with a work function set to equal or less than 4.30 eV, such as platinum, and reducing the sulfur content to less than 20 mol% on the upper electrode, along with heat treatment in hydrogen or air to remove contaminants, and incorporating alkali metals or alkaline earth metals to lower the work function and improve electron emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If cold cathode type thin film electron source is used, then device structure is simplified and integrability is improved, but electron emission surface is contaminated by sulfur, chlorine, fluorine, nitrogen, and carbon from manufacturing processes
Solution Approach 1:
Heat treatment in hydrogen atmosphere is performed before final assembly to pre-remove contaminants from the electron emission surface. This preliminary cleaning action prevents contamination from affecting electron emission characteristics during subsequent manufacturing steps.
Solution Approach 2:
Hydrogen atmosphere is used as an inert protective environment during heat treatment to prevent oxidation of the electron emission surface while removing carbon-based contaminants. The hydrogen environment protects the sensitive electron emission surface from further contamination during the cleaning process.
2Illumination intensity
If sulfur content is increased to reduce work function below 4.30 eV, then electron emission characteristics are improved, but electron emission surface becomes contaminated and brightness decreases
Solution Approach 1:
The work function parameter is precisely controlled by adjusting sulfur content within a specific range (0-20 at%) rather than simply increasing it. This parameter optimization achieves the target work function of 4.30 eV or less while preventing excessive sulfur that would cause contamination and brightness degradation.
Solution Approach 2:
Chemical substitution is employed where hydrogen atmosphere heat treatment replaces mechanical cleaning methods to remove carbon-based contaminants. The hydrogen environment chemically reacts with and removes carbon deposits without physically disturbing the electron emission surface.
3Reliability
If heat treatment in hydrogen or air is applied, then contaminants are removed and electron emission is improved, but manufacturing process complexity increases
Solution Approach 1:
The heat treatment step is merged with existing manufacturing processes such as annealing or drying steps already present in the fabrication sequence. By combining the contaminant removal function with an existing process step, no additional process complexity is introduced while still achieving improved electron emission performance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances electron emission characteristics by maintaining a low work function, reducing power consumption, and extending the life of the electron source while preventing contamination-induced degradation.
Implementation Method 1
a field emission type electron source and a hot electron type electron source
Implementation Method 2
a hot electron type thin film including a lower electrode, an upper electrode, and an electron acceleration layer provided therebetween
Implementation Method 3
heat treatment in hydrogen or air to remove contaminants
Implementation Method 4
the surface of an electron emission part is likely to be affected by contamination such as gas adsorption
Data Source
AI summary
To provide an image display device including a lower electrode, an upper electrode, and an electron acceleration layer composed of an insulator or a semiconductor provided there between, and further including a thin film electron source array that emits electrons from the upper electrode, and a phosphor surface, wherein degradation of an electron emission characteristic caused by an increase of a work function due to an adhesive material to the above-described upper electrode is suppressed. An amount of S content adhering to the upper electrode is set equal to or less than 20 mol % of a total amount of elements used as the upper electrode in terms of elements by using an element belonging to Group VIII or Group Ib or a laminated film or alloy film thereof as a component of the upper electrode of the thin film electron source.